I agree on not going cold turkey. I would gradually open door in daytime, and then cut down to one heat lamp. But, give them a place to go for a while if they do get cold. If you don't see them under the lamp, then turn it off on warm nights. Super cold nights, I'd put it back on for them. Call me a "chicken spoiler" but I love my birds and feel responsible for them. I keep one red light on in my coop. Only ones that go under it are Sultans and Silkies, but they seem to really need it. They love their "Special Place."